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1Introductione specications of production lines―such as system layout, process line length, and equipment used―in facto-ries need to be updated frequently to accommodate fre-quent change in product life cycle, production volume, product specications and manufacturing processes. ese changes are usually made gradually to minimize expenses. To maintain the productivity of these factories it is neces-sary to develop exible production lines capable of facilitat-ing these changes.Wireless communication is vital in developing exible production lines. Factories are generally equipped with machines of various ages acquired from various manufac-turers. Diverse interfaces and protocols are available for wireless communications, although they are not compatible with each other. For example, sensors are attached to leg-acy machines to collect data about quality, management, control and safety during their operation. If we use wired communication, these systems are dicult to set up, man-age and operate and may be costly.As the popularity of wireless communication use in factories increased, however, some issues were identied [7]. For example, Wi-Fi control of Automatic Guided Vehicle (AGV) may cause transfer delay of materials to the next process, if interruption or delay of control data should occur.Should such problems occur, the causes must be iden-tied and resolved to recover the production line as quickly as possible to maintain the productivity of the system. For more than two years, NICT has undertaken various experiments to evaluate the performance of wire-less communication systems installed and operating in factories (Fig.1). e objective of the evaluation is identi-cation and realization of optimized wireless control methods that are most suited to each particular use in a FiF1　A scene from the Flexible Factory Project experiment2-6 Toward Smart Factory using Wireless Communication TechnologiesSatoko ITAYACurrently wired communications are main usages in the manufacturing field, because they have a potential to realize high reliability for controlling of process machines. In recent days, however, wireless communications receive a lot of attentions based on product life cycle acceleration [1]. In a collaborative effort between private and public sectors, the National Institute of Information and Communications Technology (NICT) and member companies of Flexible Factory Project teamed up to carry out a series of tests and evaluations for wireless communications technology in several currently-operating factory sites, for the purpose of promoting the integration of IoT on the factory floor. Within a factory, there are potential instability issues in wireless communications when several different wireless systems running at the same time and location [2]-[7]. In order to tackle these issues, the project began in June 2015 and has been ongoing since. This paper shows situations of wireless environment and requirements for stable operation of manufacturing systems using wireless communication technologies.372 Terrestrial Communication Technology Research and Development